Reproductive cycles - Aquaculture

The large majority of aquaculture species are seasonal breeders, although some breed inter-mittently or continuously. Seasonal breeding is generally related to climatic seasons.

Reproductive cycles

The large majority of aquaculture species are seasonal breeders,
although some breed inter-mittently or continuously. Seasonal breeding is
generally related to climatic seasons. For example, most fresh-water fish of
temperate zones spawn in spring and early summer, but the salmonids spawn in
autumn. Rainy season and flood waters are associated with the spawn-ing of
fresh-water fishes of tropical and sub-tropical regions of Latin America and
Africa. Obviously the fishes integrate their own reproductive functions with
environmental cycles. The breeding season appears to coincide with
environmental conditions that are most conducive to the survival of the
offspring. These favourable factors, that act as cues for a suitable breeding
season, affect the central nervous system and through it the pituitary and the
gonads. Photoperiod, temperature and rainfall are important factors involved in
regulation of the reproductive cycles.

Mechanisms of reproductive timing vary very considerably among species.
For example, in salmonids that spawn in the autumn, gradually increasing
photoperiods followed by short photoperiods or decreasing photoperiods have a
major role in regulating the cycle. Temperature has an important role in the
reproductive cycle of cyprinid species. Gonadal recrudescence takes place in
Indian carps during the period of the year when both photoperiod and
temperature are increasing. Changes in the volume and velocity of water,
flooding of shallow areas and dilution or replacement of water are also
considered to be important factors. Warm temperatures and long photoperiods
appear to affect also the reproductive cycle of Chinese carps. A review of
available information would appear to show that in the majority of cases
gonadal recrudescence is regulated chiefly by seasonal variations in
photoperiod and temperature, while spawning may be controlled by temperature
and/or rainfall.

The age of sexual maturity varies widely between species. For example,
tilapia species become mature within a few months, whereas others may take a
few years. The same fish may mature earlier in a warm climate and much later in
colder climates; examples of this are the common carp and the Chinese carps.
The common carp, which takes three to four years to mature in Europe, takes
only a year to attain maturity in tropical regions. Chinese carps that take
five to seven years to mature in Europe become mature in one to three years in
tropical and subtropical conditions.

Some species have only one spawning season, during which they may spawn
several times. Others may have two or more spawning seasons. Some species of
finfish exhibit well developed parental care, which may consist of incubating
fertilized eggs in the buccal cavity of the parent, or guarding the eggs and
larvae during development. Many of the species that exhibit parental care lay
eggs in nests made of plant or other available material or in hollows dug out
on the bottomSome of the species like the Chinese and Indian carps that are
essentially riverine spawners would not spawn in the confined waters of fish
ponds or other enclosures. Their gonads develop only up to a certain stage and
then remain dormant until resorption sets in. They have however, been observed
to spawn in special types of ponds (called bundhs in India) that have a flow of
fresh rainwater, inundating shallow marginal areas where the conditions are
favourable for the fish to breed. The simulation of conditions in natural
spawning grounds may serve to induce certain fish to breed in confined areas.
The provision of nest-building material for nest-breeding species and the
provision of artificial substrates for the attachment of eggs required for
certain species are also believed to induce spawning.